Articles exhibiting durable color containing a polycarbonate, a fluorescent dye and an amine light stabilizer

ABSTRACT

An article exhibiting durable fluorescent properties comprising a polymeric matrix, dye, and hindered amine light stabilizer, wherein the polymeric matrix is comprised of polycarbonate and the dye is comprised of a dye selected from the group consisting essentially of thioxanthone, perylene imide and/or thioindigoid compounds. The article exhibits durable fluorescence which resists degradation by ultraviolet or visible radiation. The invention is optionally combined with retroreflective elements so that the resultant article has durable fluorescent properties when exposed to sunlight and is also retroreflective. A method of manufacturing an article exhibiting durable fluorescent properties is also disclosed along with a method of increasing the durability of polycarbonate in a dyed system.

This is a continuation of application Ser. No. 08/345,608, filed Nov.28, 1994, now abandoned.

FIELD OF THE INVENTION

The present invention relates to articles having increased color and/orfluorescent durability.

BACKGROUND

It is commonly known that ultraviolet radiation causes colorants todegrade. This is a particularly acute problem for articles exposed tosolar radiation for extended periods of time such as articles placedoutdoors. Color degradation occurs in articles colored with conventionalcolorants as well as articles colored with fluorescent colorants.However, this is a particularly acute problem for fluorescent articles.Fluorescent dyes degrade, often turning colorless more quickly thanconventional colorants. The effective life of fluorescent materialsexposed to daily solar radiation is short and is typically measured interms of days or months. In contrast, the life of conventionally coloredmaterials is usually substantially longer and is typically measured inyears.

If increased visibility of an article is desired, the article is oftencolored with fluorescent colorants even though fluorescent colorants areless durable than conventional colorants. Fluorescent colors allowenhanced visibility because the visual contrast that the fluorescentcolors create with the environment make the materials more conspicuousthan ordinary nonfluorescent articles. An example of one industry whichbenefits from using fluorescent colorants is the traffic sign industry.Fluorescent colored traffic signs are effective at increasing thevisibility of the signs which increases motorist safety. Even thoughfluorescent signs increase motorist safety, their use has been limiteddue to their poor color stability and the need to frequently replacethem to maintain effective performance.

At ground level, solar radiation comprises electromagnetic radiationhaving wavelengths longer than about 290 nanometers, with the range fromabout 400 to about 700 nanometers typically considered the visible lightrange. Radiation having shorter wavelengths than visible light isbelieved to be damaging to both conventional and fluorescent colorants.Attempts to maintain color of a fluorescent article have included addingultraviolet screens which selectively filter radiation below the 340 nmto 380 nm range. Japan Kokai No. 2-16042, Application No. 63-165914(Koshiji, et al.) discloses fluorescent articles comprising a screenlayer and a layer containing a fluorescent coloring agent wherein thescreen layer only permits a defined range of light transmission.European Patent Application No. 91311189.4 also discloses aretroreflective article comprising an ultraviolet screening layer and acolor layer contained in a defined polymeric matrix. The articleexhibits durable daylight fluorescence and resistance to degradationfrom exposure to sunlight.

Articles which exhibit enhanced fluorescence and color durability, evenwhen exposed to ultraviolet radiation, are needed. In particular,fluorescent articles which retain their color and/or their fluorescentproperties without requiring the use of protectant overlays are needed.

SUMMARY OF THE INVENTION

The present invention provides, in brief summary, articles which exhibitboth enhanced color durability and fluorescing properties with orwithout the use of protectant overlays. That is, the articles of theinvention retain their color and are able to fluoresce for a longerperiod than is normally expected even when the articles are exposed todirect sunlight. The invention further includes a method to manufacturesuch durable fluorescent articles. Also included is a method ofincreasing the durability of polycarbonate in a dyed system.

Articles of the invention comprise (1) polymeric matrix, (2) dye, and(3) hindered amine light stabilizer, wherein the polymeric matrix iscomprised of polycarbonate and the dye contains at least one the ofcompounds selected from the group of thioxanthone, perylene imide, andthioindigoid dyes. The hindered amine light stabilizer is comprised ofcompounds from the 2,2,6,6-tetraalkyl piperidine class of compounds in apreferred embodiment.

In one embodiment, articles of the present invention also includeretroreflective elements. The resulting articles exhibit retroreflectiveand durable color and/or durable fluorescent properties. Such materialsexhibit enhanced daytime and nighttime visibility over the course ofextended outdoor exposure.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is further explained with reference to the drawings,wherein:

FIG. 1 is a cross-sectional view of an embodiment of the inventionincluding retroreflective elements,

FIG. 2 is a cross-sectional view of an alternate embodiment of theinvention including retroreflective elements,

FIG. 3 is a cross-sectional view of an alternate embodiment of theinvention including retroreflective elements, and

FIG. 4 is a cross-sectional view of an alternate embodiment of theinvention including an ultraviolet protectant overlay andretroreflective elements.

These figures, which are idealized, are not to scale and are intended asmerely illustrative and non-limiting.

DEFINITIONS

As referred to herein, the term "colorant" shall mean pigment or dyes orother substances used to impart hue and chroma and value to an article.

As referred to herein, the term "conventional colorant" shall meancolorants which do not exhibit fluorescent properties to the unaidedeye.

As referred to herein, the term "durable" shall refer to an enhancedretention of color or fluorescence upon exposure to weathering.

As referred to herein, the term "hindered amine light stabilizer" refersto sterically hindered amines of the class of compounds typicallyrepresented by 2,2,6,6 tetraalkyl piperidines.

As referred to herein, the term "weathering" shall mean exposing anarticle to either natural or artificial environments which include heat,light, moisture, and ultraviolet radiation.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS OF THE INVENTION

The present invention combines a polymeric matrix containing dye andhindered amine light stabilizer to create an article which exhibitsenhanced color durability and/or more durable fluorescence. Thepolymeric matrix of the invention is first discussed followed by adiscussion of suitable dyes and of suitable hindered amine lightstabilizers.

Polymeric Matrix

Polycarbonate is the preferred polymeric matrix of the invention becauseit is substantially transparent and is easily colored with fluorescentand conventional dyes. Additionally, polycarbonate exhibits good opticalproperties such as good light transmittance which is important for thepresent invention. Even though polycarbonate exhibits these desirablecharacteristics, it is surprising that polycarbonate is the polymericmatrix of choice for the present invention. As is commonly known in theart, polycarbonate is photosensitive and degrades when exposed toultraviolet radiation.

Dye

In a preferred embodiment the fluorescent dyes of the invention are dyesfrom the thioxanthone, perylene imide and thioindigoid classes ofcompounds. The invention anticipates that a single fluorescent colorantor dye may be used to color an article of the invention or that acombination of one or more fluorescent colorants and one or moreconventional colorants may be used.

Typically, between about 0.01 and about 2.00 weight percent, andpreferably between about 0.05 and about 0.70 weight percent and mostpreferably between about 0.1 and about 0.5 weight percent of fluorescentdye is contained in the article of the present invention. It will beunderstood that articles with dye loadings outside this range can beused in accordance with the invention. Although dye loading may varydepending upon the final application, these loadings are typical forabout a 0.075 to 0.25 mm thick film. However, if the dye is added to athicker film, lower dye loadings can give the same visual effect. Asknown by those in the art, articles having heavier dye loadings willexhibit brighter fluorescence and/or deeper color than will articleswith lighter dye loadings of the same dye. However, articles having veryhigh fluorescent dye loadings may exhibit a self-quenching phenomenonwhich occurs when molecules of the fluorescent dye absorbs the energyemitted by neighboring fluorescent dye molecules. This self-quenchingcauses an undesirable decrease in fluorescent brightness.

In some embodiments, the colorant in the articles of the presentinvention will consist essentially of one or more dyes selected from theperylene imide, thioindigoid and thioxanthone classes of compounds. Inother instances, the article may also contain other coloring agents suchas pigments or other dyes in addition to those described to adjust thecolor and appearance of the article. For example, polycarbonatetypically has a yellow cast. Minor amounts, e.g., about 0.01 weightpercent or less, of pigments sometimes referred to as "bluing agents"may be incorporated to neutralize the yellow appearance. Othernon-fluorescent or conventional dyes or pigments may also be added tothe present invention, however, care should be taken in selecting suchdyes and dye loadings so that the dyes do not significantly interferewith the performance of the fluorescent dyes. If retroreflectiveelements are included in the article of the present invention, any dyesor pigments should not undesirably impair the transparency of thearticle as such would impair the retroreflective properties of thearticle.

Hindered Amine Light Stabilizers

Hindered amine light stabilizers (HALS) are included in the article ofthe present invention. This is a somewhat surprising combinationbecause, as one skilled in the art will recognize, it is not recommendedto combine amines with polycarbonate. It has traditionally been knownthat amines attacked the carbonyl group of the polycarbonate, therebydegrading the polycarbonate (for example see Schnell, Chemistry andPhysics of Polycarbonates, page 183, 1964).

Without intending to be bound by theory, it is believed that thecombination of the sterically hindered amine, the polycarbonate matrixand the dye in the present invention prevents an as yet undefineddegradation and/or reaction between the dye and the polycarbonate whichcould otherwise occur. Insofar as we know, the advantages of the presentinvention are attained through the combination of dye, polymer matrixmaterial, and hindered amine light stabilizer described herein. The dyesin the present invention are thought to act as singlet oxygensensitizers. Energy transfer, which generally occurs from the tripletstate of the dye, is quenched by ground state molecular oxygen toproduce active singlet oxygen. The singlet oxygen is then free to reactwith the dye, causing dye degradation. Alternatively, the singlet oxygenmay react with the polymer, leading to degradation of the polycarbonate.However, the hindered amine light stabilizer present in the invention iscapable of directly quenching the singlet oxygen formed, preventinginitiation of the degradation reactions. The hindered amine lightstabilizers can also prevent secondary reactions initiated by polymeroxidation from proceeding. These reactions include a number of radicalor peroxide-based chain reactions that are thought to occur in thephoto-oxidation of polycarbonate which can result in polymer and dyedegradation. Preventing these reactions increases the durability of thepolycarbonate and the dye in the dyed system.

Any hindered amine light stabilizer is suitable for the presentinvention such as 2,2,6,6 tetraalkyl piperidine compounds but preferably2,2,6,6 tetramethyl piperidine compounds are employed as the hinderedamine light stabilizers due to the ready availability of the compounds.The hindered amine light stabilizers are included in articles of thepresent invention from about 0.05 to about 1.00 weight percent andpreferably from about 0.10 to about 0.75 weight percent and mostperferably from about 0.1 to about 0.5 weight percent.

Retroreflection

As previously stated, in some embodiments articles of the presentinvention are retroreflective. Such retroreflective capability isimportant when using the present invention to make traffic signs. FIG. 1illustrates how retroreflective capability can be achieved in thepresent invention by forming retroreflective elements 30 on one side ofa film 32 containing the polymeric matrix/hindered amine/dye composite.FIGS. 2 and 3 illustrate alternate retroreflective embodiments of theinvention. A retroreflective base sheet 12 or 40 is attached to a sheet18 or 50 of the present invention by either mechanically laminating theretroreflective base sheet and the invention sheet directly to eachother, or by attaching the two sheets with a transparent adhesive. If anadhesive is used, the adhesive is preferably substantially transparentto visible light. As shown in FIG. 2, the retroreflective base sheet maycomprise cube-corner retroreflective elements 20 formed on the back sideof the sheet. Other embodiments include a base sheet 40 havingmicrosphere-based retroreflective structures 52 as illustrated in FIG.3. A monolayer of microspheres 71 is embedded in binder layer 70 withspace layer 72, specular reflective layer 74 and optional adhesive 76.Examples of retroreflective elements are disclosed in U.S. Pat. Nos.4,896,943 and 5,069,964 (both microsphere-based structures) and U.S.Pat. No. 4,938,563 (cube-corner reflector structure) which are allherein incorporated by reference.

Ultraviolet Protectant Overlays

Although not necessary, articles of the present invention may optionallyinclude an overlay which may or may not include ultraviolet absorbingagents. Some additional improvement in resisting degradation is observedwhen the article of the present invention is covered by an overlayincluding ultraviolet absorbing agents and is exposed to sunlight. Theoverlay is preferably substantially transparent to visible light andincludes a means to screen substantial portions of incident ultravioletradiation. FIG. 4 illustrates a retroreflective embodiment of thepresent invention similar to that shown in FIG. 2 and further includingan overlay 56. The polymeric matrix/dye/hindered amine light stabilizercomposite is shown as a film 60 and is laminated to a cube-cornerretroreflective sheet 64. The overlay 56 is preferably coextensive withthe composite film 60 so as to provide the most protection to theinvention film 60.

EXAMPLES

The invention is further explained by the following illustrativeexamples which are intended as nonlimiting. Unless otherwise indicated,all amounts are expressed in parts by weight.

The following abbreviations are used in the examples:

    ______________________________________                                        Abbreviation Meaning                                                          ______________________________________                                        PC           Polycarbonate;                                                   PMMA         Polymethylmethacrylate;                                          SO63         HOSTASOL RED GG ™                                                          Solvent Orange 63                                                             thioxanthone dye from                                                         Hoechst Celanese;                                                Vat 41       HOSTASOL RED 5B ™                                                          Red 41 thioindigoid dye                                                       from Hoechst Celanese;                                           PI 240       LUMOGEN F240 ™ Orange -                                                    perylene imide dye from                                                       BASF;                                                            SY 160:1     MACROLEX 10GN ™ Solvent                                                    Yellow 160:1 benzoxazole                                                      coumarin dye from Mobay                                                       Corp.                                                            SG 5         FLUOROL GREEN GOLD 084 ™                                                   Solvent Green 5 perylene                                                      dye from BASF.                                                   HALS 1       Dimethyl succinate                                                            polymer with 4-hydroxy-                                                       2,2,6,6-tetramethyl-1-                                                        piperidine ethanol                                                            available as TINUVIN 622                                                      from Ciba-Geigy Corp,                                                         Hawthorne, NY.                                                   HALS 2       Poly [6[(1,1,3,3-                                                             tetramethybutyl)amino]-                                                       s-triazine-2,4-diyl]                                                          [2,2,6,6-tetramethyl-4-                                                       piperidyl)imino]                                                              hexamethylene [(2,2,6,6-                                                      tetramethyl-4-piperidyl)                                                      imino)] available as                                                          CHIMASORB 944FL from                                                          Ciba-Geigy Corp.                                                 HALS 3       bis (2,2,6,6-Tetramethyl-                                                     4-piperidinyl) sebacate                                                       available as TINUVIN 770                                                      from Ciba-Geigy Corp.                                            ______________________________________                                    

Unless otherwise indicated, the following test methods were used.

Accelerated Weathering

In order to simulate outdoor exposure to sunlight on an acceleratedbasis, the samples in Examples 1 through 6 and 8 were exposed inaccordance to ASTM G 26 - Type B, Method A, with a water-cooled xenonarc device with borosilicate inner and outer filters for periods of 102minutes of exposure at a Black Panel temperature of about 63° C.followed by 18 minutes of exposure while subjecting the sample todeionized water spray. One thousand hours exposure in this cycle isbelieved equivalent to at least several months exposure to directoutdoor sunlight.

Color

Color was determined by the following technique.

A Labscan 6000 Spectrophotometer from Hunter was used at the followingsettings and conditions:

Illuminant D₆₅,

0/45 Geometry,

25 millimeter port,

CIE 2 Degree Standard Observer,

with measurements taken every 10 nanometers over a range of 400 to 700nanometers.

Percent of Initial Peak Total Spectral Radience Factor (% PTSR) wascalculated as the ratio, in percent, of peak total spectral radiancefactor of the sample after exposure for the indicated time (time t) tothe peak total spectral radiance factor of an unexposed sample at thewavelength of the initial peak total spectral radiance. This is betterillustrated by the following equation. ##EQU1##

Peak total spectral radiance factor is a relative measure of thefluorescence content. Fluorescence content is directly correlated to theamount of fluorescent dye, therefore, peak reflectance is a relativemeasure of the fluorescent dye content remaining. Difference in % PTSRof about 5 or less are generally not considered as significant formeasurements made on constructions.

The CIELAB color difference, (or DE*), between the sample after exposurefor the indicated period of time and the unexposed sample wasdetermined. DE* is a function of several color vector components. Forpurposes of reference only, a DE*, or color change of about 2 units isjust detectable by the naked eye whereas a DE* of 20 or greaterrepresents a substantial color change.

Retained Fluorescence

Fluorescence was measured using a SLM AB2 Luminescence Spectrophotometer(SLM Instruments, Rochester, N.Y.) using a 150 watt continuous Xenonlamp.

Retained Fluorescence was calculated as the ratio, in percent, offluorescent intensity of the sample after exposure for the indicatedlength of time to the fluorescent intensity of an unexposed sample, atthe wavelength of peak emission of the unexposed sample.

Molecular Weight

Molecular weight was measured by gel permeation chromatography (GPC)using a set of MICROSTYRAGEL brand columns available from WatersDivision of Millipore Corp, Milford, Mass. and polystyrene standards forcalibration. Samples were dissolved and run in tetrahydrofuran at 30° C.at a flow rate of 1.0 milliliter per minute. A UV detector set at 266 nmwas used for detection of polycarbonate.

Exterior Weathering

Exterior weathering was done on samples about 7×12 centimeters in size.The samples were adhered to an aluminum coupon which was mounted on ablack painted panel facing upward at 45° from vertical and facing south.The samples were exposed for 12 months in Wittmann, Ariz.

Determining Time to 50% Dye Loss

Films were mounted onto aluminum slide frames, overlaid with anultraviolet transparent polyolefin film which was a 2 mil (0.005 cm)thick film of an ethylene/acrylic acid copolymer made from Primacor 3440available from Dow Corporation of Midland, Mich. and exposed inaccordance with ASTM G26, Type B, Method A, as described earlier.

The dye concentration in each sample was measured initially and afterevery 500 hours exposure. The samples were exposed for a total of 2000hours. The Time-to-50%-Dye-Loss for each sample was graphicallyinterpolated from plots of dye concentration versus total exposure (ie.[SO63] vs Hours).

Dye concentrations were determined from UV-Visible spectroscopicmeasurements of the sample films using the Beer-Lambert Law. Allmeasurements were made on a Beckman Model DU-70 UV VisibleSpectrophotometer.

Example 1

Example 1 illustrates the improved durability of fluorescent propertiesand color of fluorescent dye SO63 with a hindered amine light stabilizerand compares the durability of a sample with a sample including anultraviolet protectant overlay.

Films were prepared for Example 1 as follows. The fluorescent dye andHALS (if present) were blended with polycarbonate resin pellets. Thefluorescent dye was added to the polycarbonate resin pellets at 0.2weight percent loading. The hindered amine light stabilizer, if present,was incorporated into the mixture at 0.26 wt % loading. The resinpellets used were Makrolon FCR-2407 available from Miles Inc. ofPittsburgh, Pa. The dye/resin/HALS mixture was dried overnight to removemoisture. After drying overnight, the mixture was extruded into film ofabout 4-6 mils (0.1-0.15 mm) thick using a single screw extruder withthree heating zones set at 260° C., 260° C. and 304° C. and a film dieset at 304° C. The extruder was a 3/4 inch single screw extruder for theHaake Rheocord as available from Haake of Karlsruhe, Germany.

The film was then laminated onto 3M Brand Scotchlite™ Diamond GradeRetroreflective Sheeting 3970G construction (as manufactured by 3MCompany of St. Paul, Minn.) using a transparent acrylic adhesive. Anoverlay film consisting of urethane-acrylic film with or without a UVabsorber as (indicated in the Table 1) was laminated over thefluorescent/retroreflective construction with acrylic adhesive.

The hindered amine light stabilizer (HALS) used for Example 1 sampleswas HALS 1 (Tinuvin 622), an oligomeric tertiary amine. Comparable filmswithout HALS were also prepared as described earlier and laminated toform samples having a fluorescent/retroreflective/overlay constructionsand all samples were weathered in accelerated test devices as describedabove. Fluorescence and color retention were assessed by colormeasurements on the Hunter Labscan 6000. Fluorescence durability iscorrelated to % PTSR and color change is calculated by DE* describedabove.

                  TABLE 1                                                         ______________________________________                                                          % of Initial Peak Spectral                                                    Radiance Factor                                                       UV      Accelerated exposure in Hours                               Sample.sup.1                                                                         HALS.sup.2                                                                             Absorber.sup.3                                                                          500  1000  1500  2000                               ______________________________________                                        1-A    Yes      No        86%  80%   68%   61%                                1-B    No       No        80%  60%   54%   43%                                1-C    Yes      Yes       90%  84%   80%   63%                                1-D    No       Yes       87%  73%   63%   46%                                ______________________________________                                         .sup.1 All Samples contained dye SO63 at 0.2 wt % loading                     .sup.2 HALS 1 at 0.26 wt % loading                                            .sup.3 UV absorber was Uvinol 400 from BASF at 3 wt % loading.           

                  TABLE 2                                                         ______________________________________                                                     DE* of Samples Exposed 1000                                                   Hours to Accelerated Exposure as                                              Compared to Unexposed Samples                                    Sample.sup.1                                                                         HALS.sup.2                                                                            UVA.sup.3                                                                             500   1000   1500  2000                                ______________________________________                                        1-A    Yes     No      5.7   12.4   26.6  38.2                                1-B    No      No      9.9   30.7   35.8  53.8                                1-C    Yes     Yes     4.9   13.1   17.8  47.2                                1-D    No      Yes     5.5   23.0   32.1  58.6                                ______________________________________                                         .sup.1 All samples contain dye SO63 at 0.2 wt % loading                       .sup.2 HALS 1 at 0.26 wt % loading                                            .sup.3 Urethaneacrylic overlay with 3% Uvinol 400 (UV absorber) in            overlay.                                                                 

The results shown in Tables 1 and 2 illustrate that the HALS offers asubstantial improvement in fluorescence and color durability of SO63with or without an ultraviolet protectant overlay. The samplescontaining HALS showed an improvement in color and fluorescencedurability as compared to those samples without HALS. Additionally, animprovement was observed in the HALS-containing samples when a UVabsorbing overlay was added to the sample.

Example 2

Example 2 illustrates the improved durability of fluorescent propertiesof dye RED41 in articles of the present invention.

Samples 2E through 2H of Example 2 were prepared as described in Example1 except that the polycarbonate resin used was Lexan 123R-112 asavailable from GE Plastics of Mt. Vernon, Ind. The hindered amine lightstabilizer used for the samples in Example 2 was HALS 1. Samples wereweathered using accelerated-weathering devices for the time periodsnoted. The results are recorded in Table 3 below.

                  TABLE 3                                                         ______________________________________                                                     % of Initial Peak Total                                                       Spectral Radiance Factor                                                      For exposure in Hours                                            Sample.sup.1                                                                             HALS.sup.2                                                                            UVA.sup.3   500  1000                                      ______________________________________                                        2-E        No      No          81%  53%                                       2-F        Yes     No          76%  63%                                       2-G        No      Yes         92%  62%                                       2-H        Yes     Yes         91%  77%                                       ______________________________________                                         .sup.1 Samples 2E-2H include dye Red 41 at 0.2 wt % loading                   .sup.2 HALS 1 at 0.26 wt % loading.                                           .sup.3 Urethaneacrylic overlay with 3% Uvinol 400.                       

The results shown in Table 3 show that the dye RED41 benefits by addingHALS1 (Samples 2-F and 2-H)

Example 3

Example 3 illustrates different hindered amine stabilizers at differentloadings are suitable for increasing the durability of fluorescent dyeSO63.

Films were prepared as described in Example 1. The amount and type ofHALS and dye added to each film is designated in Table 4 below. TheSamples were exposed in an accelerated weathering device as describedearlier.

                  TABLE 4                                                         ______________________________________                                                  Film    Initial            Time to                                            Caliper Weight %   Additive/                                                                             50% Dye                                  Sample*   (mm)    SO63       Weight %                                                                              Loss                                     ______________________________________                                        CONTROL   0.1     0.2        None    420 hours                                3A        0.1     0.2        HALS 2/ 800 hours                                                             0.25%                                            3B        0.1     0.2        HALS 2/ 740 hours                                                             0.5%                                             3C        0.1     0.2        HALS 1/ 550 hours                                                             0.5%                                             ______________________________________                                    

The results in Table 4 illustrate that different hindered amine lightstabilizers, including HALS 2 and HALS 1, are effective at increasingthe durability of SO63 fluorescent dye.

Example 4

Example 4 illustrates a range of dye loadings is suitable for thepresent invention.

Samples were prepared as described in Example 3. Dye SO63 and HALS 1were used to prepare the samples. In samples containing HALS, 0.50 wtpercent HALS 1 was included. The amount of dye added to each sample islisted below. The samples were weathered by exposing them to acceleratedweathering.

                  TABLE 5                                                         ______________________________________                                                  Film    Initial            Time to                                            Caliper Weight %   HALS/   50% Dye                                  Sample    (mm)    SO63       Weight %                                                                              Loss                                     ______________________________________                                        CONTROL   0.1     0.2        None    420 hours                                3C        0.1     0.2        HALS 1/ 550 hours                                                             0.5%                                             4A        0.1     0.4        HALS 1/ 570 hours                                                             0.5%                                             ______________________________________                                    

The results in Table 5 demonstrate that HALS is effective at differentdye loadings.

Example 5

Example 5 illustrates different hindered amine light stabilizers with arange of loadings are suitable for the present invention.

Films were prepared as described in Example 1. The resin used wasMakrolon FCR-2407 from Miles Incorporated of Pittsburgh, Pa. Sampleswere prepared by hot laminating the colored films to a clear layer withretroreflective elements embossed in a second side and hot laminating aPMMA overlay layer to the first side of the colored films. All coloredfilms contained dye SO63 at 0.20 weight percent. HALS 1 was added to thefilms as designated in Table 6 below. The samples were weathered byexposing them in an accelerated device for 1000 hours. Results are shownin Table 6.

                  TABLE 6                                                         ______________________________________                                                 % PTRSF and DE* for Accelerated                                               Weathering for 1000 Hours                                                   [SO63]           [HALS]                                                Sample wt %    HALS     wt %    DE*   % PTSRF                                 ______________________________________                                        5A     0.2     --       0       17.3  75%                                     5B     0.2     HALS 1   0.1     9.8   89%                                     5C     0.2     HALS 1   0.25    5.9   89%                                     5D     0.2     HALS 1   0.5     6.8   90%                                     ______________________________________                                    

The results illustrate HALS 1 is effective at a variety of loadings forincreasing the durability of the fluorescent properties of dye SO63.

Comparative Example 6

Comparative Example 6 illustrates polymethyl methacrylate is not asuitable polymeric matrix for manufacturing articles of the presentinvention because such articles do not exhibit increased durability offluorescent properties or color.

The films for Comparative Example 6 were prepared as described inExample 1 except the polymeric matrix used was polymethyl methacrylate(PMMA) instead of polycarbonate. The PMMA used was either Perspex CP924or CP923 from ICI Acrylics (St. Louis, Mo.) or Lucite 47 K from Dupont(Wilmington, Del.), all contained roughly 0.3 wt % UV absorber of abenzotriazole type. The HALS used (if any) was HALS 1 added at a loadingof 0.25 weight percent. Extrusion temperatures for the PMMA were 249° to260° C. Samples were prepared by hot laminating either four 3 mil (0.075mm) colored films or two 6 mil (0.15 mm) colored films together andembossing retroreflective elements on the second side of the laminatedconstruction. The samples were weathered by exposing them to acceleratedweathering for the times listed in Table 7.

                  TABLE 7                                                         ______________________________________                                               % of Initial Peak Total Spectral Radiance                                     Factor for Exposure in Hours for PMMA.sup.1                            Sample   Dye.sup.2                                                                             HALS.sup.3 500 Hrs                                                                              1000 Hrs                                   ______________________________________                                        6A       SO63    Yes        74%    72%                                        6A-1     SO63    No         85%    78%                                        6B       Red 41  Yes        66%    61%                                        6B-1     Red 41  No         70%    63%                                        6C       PI 240  Yes        93%    92%                                        6C-1     PI 240  No         89%    90%                                        ______________________________________                                         .sup.1 Polymethyl methacrylate                                                .sup.2 Dye was added to the samples at a loading of 0.20 weight percent       except sample 6C1 which was at 0.29 weight percent                            .sup.3 HALS 1 was added at 0.25 wt percent                               

As discussed above, no increase of fluorescence or color durability isobserved (Table 7) when adding a HALS and a fluorescent dye topolymethyl methacrylate.

Example 7

Example 7 illustrates that polycarbonate is more durable if a hinderedamine light stabilizer is included along with the polymeric matrix and afluorescent dye.

The samples for Example 7 were prepared as described in Example 5. Theresin used was Makrolon FCR-2407 from Miles Inc. Dye SO63 was added tothe samples at a loading of 0.2 weight percent. The hindered amine lightstabilizer and the amount added to each sample is listed below in Table8. The samples were weathered by exterior exposure for 12 months asdescribed above.

                  TABLE 8                                                         ______________________________________                                                      Polycarbonate        Peak Total                                               Number Average                                                                             DE*     Spectral                                           Weight                                                                              Molecular Weight                                                                           (vs     Factor Re-                                 Sam-          %       Unex- Ex-    Unex- tained (%                            ple  HALS     HALS    posed posed  posed)                                                                              of Initial)                          ______________________________________                                        Con- None     0       17,796                                                                              12,058 62    55                                   trol                                                                          7-A  HALS 2   0.25    17,687                                                                              15,865 19    87                                   7-B  HALS 2   0.50    17,836                                                                              15,552 20    87                                   7-C  HALS 3   0.50    17,934                                                                              15,311 35    77                                   ______________________________________                                    

The molecular weight results shown in Table 8 illustrate thepolycarbonate and fluorescent dye samples containing HALS did notdegrade as readily as the control which did not contain HALS. Thus, thepresent invention helps to increase the durability of polycarbonate.

The results in Table 8 further show that the colors and the fluorescentproperties in the samples containing the HALS did not change color asreadily as the samples which did not contain the HALS.

Example 8

Example 8 illustrates the effect of several different hindered aminelight stabilizers on fluorescent color durability on outdoor exposure.

Samples were prepared as in Example 5, except that a second color layerwas used in place of the clear layer and it was embossed withretroreflective elements. The resin used was Makrolon FCR-2407 fromMiles Inc. All colored films contained dye SO63 at 0.25 wt percent inpolycarbonate, the hindered amines added are designated in Table 9 andwere added at 0.25 wt percent. The samples were exposed in Arizona for 1year as described earlier and measurements were taken for Percent ofInitial Peak Total Spectral Radiance and color change. The color changeresults are given in Table 9.

                  TABLE 9                                                         ______________________________________                                        Arizona Exposure 12 months                                                                                    Color Change                                  Sample  HALS ADDED   % PTSRF    (DE*)                                         ______________________________________                                        Control None         43         48                                            8-A     HALS 1       70         21                                            8-B     HALS 2       83         9.6                                           8-C     HALS 3       89         14                                            ______________________________________                                    

Example 9

Example 9 illustrates the enhanced fluorescence durability of samples ofthe present invention as measured by a spectrofluorometer. Samples wereprepared as in Example 5 and exposed to accelerated weathering. Readingswere taken initially and at 2500 hours. The HALS, the dye and therespective loadings are listed in Table 10 below along with the results.

                  TABLE 10                                                        ______________________________________                                                         Dye      % Retained    %                                     Sample [HALS]    [SO63]   Fluorescence                                                                           DE*  PTSRF                                 ______________________________________                                        Control                                                                              0         0.2 wt % 31%      68.6 48%                                   9A.sup.1                                                                      9B.sup.1                                                                             HALS 2/   0.2 wt % 78%      34.8 77%                                          0.25 wt %                                                              Control                                                                              0         0.2 wt % 26%      71.3 42%                                   9C.sup.2                                                                      9D.sup.2                                                                             HALS 3/   0.2 wt % 81%      32.3 81%                                          0.25 wt %                                                              ______________________________________                                         .sup.1 Polycarbonate was comprised of Makrolon 2407                           .sup.2 Polycarbonate was comprised of 80% Makrolon 2407 and 20% Lexan 123                                                                              

Comparative Example 10

Comparative Example 10 illustrates that fluorescent dyes SY 160:1 and SG5 are not suitable dyes for the present invention. Films were preparedas described in Example 1. Samples 10A, 10B and 10D were prepared by hotlaminating two 4 mil (0.1 mm) colored films together. A 2 mil PMMAoverlay containing 1.8% Tinuvin 327 (UV absorber available fromCiba-Geigy) was hot laminated to a first side of the colored laminate.Sample 10C was prepared by hot laminating a 3 mil PMMA overlaycontaining 1.2 weight percent Tinuvin 327 to a first side of a 12 mil(0.3 mm) film and embossing retroreflective elements in the second sideof the film. The polycarbonate resin used in Samples 10A and 10B wasMakrolon 2407 and Lexan 123R-112 was used in Samples 10C and 10D.

Samples 10E and 10F are samples which are provided for comparisonpurposes. Samples 10E and 10F are prepared according to the presentinvention and demonstrate that perylene imide dyes are suitable for usein the present invention. Sample 10E was formed from polycarbonate resinLexan 123R-112. A 12 mil polycarbonate film was formed with a 3 mil(0.075 mm) PMMA overlay hot laminated to the first side of the coloredfilm with retroreflective elements embossed into the second side of thecolored film. Sample 10-F was formed from polycarbonate resin Lexan123R-112. The sample was prepared by hot laminating two 4 mil (0.10 mm)colored films together and by laminating a 2 mil (0.05 mm) PMMA overlayto a first surface of the resulting colored film. Retroreflectiveelements were embossed into the second surface of the colored film. Theoverlays for samples 10-E and 10-F were made to have the same UVscreening ability. The 3 mil (0.75 mm) overlay included 1.2 wt % Tinuvin327 as available from Ciba Geigy Corp. while the 2 mil (0.05 mm) overlaycontained 1.8 wt % Tinuvin 327. The HALS used for all the samples wasHALS1. The samples were weathered by exposing them to acceleratedweathering. Results are given in Table 11.

                  TABLE 11                                                        ______________________________________                                                 [DYE]     [HALS]                                                     Sample   wt %      wt %     1000   1500 2000                                  ______________________________________                                        10A      SY160:1   --       82%    79%  67%                                            0.2                                                                  10B      SY160:1   0.25     84%    80%  66                                             0.2                                                                  10C      SG 5      --       50%    44%  --.sup.1                                       0.2                                                                  10D      SG 5      0.26     46%    42%  --.sup.1                                       0.2                                                                  10E      PI 240    --       83%    --.sup.2                                                                           76%                                            0.2                                                                  10F      PI 240    0.26     94%    --.sup.2                                                                           88%                                            0.2                                                                  ______________________________________                                         .sup.1 Data was not measured because of the severe color degradation          .sup.2 Samples were not measured at 1500 hour interval.                  

One skilled in the art will recognize that details of the previousembodiment may be varied without departing from the spirit and scope ofthe invention.

We claim:
 1. An article exhibiting durable color and/or fluorescentproperties comprising polymeric matrix, dye and hindered amine lightstabilizer, wherein the dye contains at least one of the dyes selectedfrom the group of thioxanthone, perylene imide and thioindigoidcompounds and polymeric matrix comprises polycarbonate.
 2. The articleof claim 1 wherein the article is retroreflective.
 3. The article ofclaim 1 wherein the article is a film.
 4. The article of claim 3 furthercomprising a retroreflective sheet disposed on one side of said film. 5.The article of claim 3 wherein the article is sufficiently flexible tobe wound about a mandrel having a diameter of about 1 centimeter.
 6. Thearticle of claim 1 wherein the article contains about 0.01 to about 2.00weight percent of said dye.
 7. The article of claim 1 wherein saidarticle contains about 0.10 to about 0.75 weight percent of saidhindered amine light stabilizer.
 8. The article of claim 5 wherein saidarticle contains about 0.05 to 0.70 weight percent of said hinderedamine light stabilizer.
 9. The article of claim 5 wherein said articlecontains about 0.1 to 0.5 weight percent of said hindered amine lightstabilizer.
 10. The article of claim 5 wherein the retroreflective sheetcomprises a monolayer of transparent microspheres and reflective meansdisposed on one side of said microspheres.
 11. The article of claim 1wherein said hindered amine stabilizer is comprised of a2,2,6,6-tetramethyl piperidine compound.
 12. The article of claim 1further including an overlay.
 13. A method of manufacturing an articleexhibiting durable color and/or fluorescent properties,comprising:extruding a polycarbonate matrix comprising about 0.01 toabout 2.0 weight percent of at least one dye selected from the groupconsisting of thioxanthone, perylene imide, and thioindigoid compoundsand about 0.05 to about 1.00 weight percent of a hindered amine lightstabilizer.
 14. The method of claim 13 wherein the hindered amine lightstabilizer is comprised of a compound from the class of 2,2,6,6tetramethyl piperidine compounds.
 15. The method of claim 13 wherein thedye is present at a loading of between about 0.05 and about 0.70 weightpercent.
 16. The method of claim 13 wherein the hindered amine lightstabilizer is present in an amount of between about 0.10 to about 0.50weight percent.
 17. The method of claim 13 further including extrudingsaid polycarbonate matrix/dye/hindered amine light stabilizer compositeinto a film and laminating said film onto retroreflective sheeting. 18.The method of claim 13 further including laminating an overlay to saidfilm.
 19. A method of increasing the durability of polycarbonatecomprising combining polycarbonate with hindered amine light stabilizerand dye wherein the dye contains at least one of the dyes selected fromthe group of thioxanthone, perylene imide and thioindigoid compounds.20. The method of claim 19 wherein the hindered amine light stabilizeris a 2,2,6,6-tetramethyl piperidine compound.
 21. The method of claim 19wherein the dye is present at a loading of between about 0.05 and about0.70 weight percent and the hindered amine light stabilizer is presentat a loading of between about 0.05 and about 1.00 weight percent.
 22. Afilm having a first and a second side which exhibits durable colorand/or fluorescent properties comprising polymeric matrix, dye andhindered amine light stabilizer, wherein the dye contains at least oneof the dyes selected from the group of thioxanthone, perylene imide andthioindigoid compounds and the polymeric matrix comprises polycarbonateand further wherein retroreflective elements are disposed on one side ofsaid film and an overlay is disposed on said second side of said film.